The present invention relates to a fluid level detection system and method. More particularly, the present invention relates to a fluid level detection system and method for use in a printing device that determines the volume of fluid in a replaceable or refillable printing fluid container, such as that used in inkjet printing, based upon the volume of air in a pressure chamber having a volume which surrounds the container.
As with may items which are consumed during use, such as gasoline in a car, it is desirable for a user of a printing device to know how much printing fluid or printing composition (e.g., ink or toner) remains in a replaceable or refillable container. Printing devices which only provide an end-of-life or out-of-printing fluid indication do not give the user sufficient warning before printing stops. Also, if a printing device with only out-of-printing fluid detection is used for unattended printing, the user has no way of ensuring that there is sufficient printing fluid in a partially used container to complete a printing job. For a large unattended print job, the user may choose to replace all of the printing fluid containers with new ones to ensure that none of them run out during printing. After the job is complete, the previous containers which still have some printing fluid may be placed back into the printing device. In this case, multiple containers with varying printing fluid amounts are in use, making it difficult to know how much printing fluid is in each container. It is desirable for the printing device user to know at all times how much printing fluid is in each container installed in the printing device.
Traditional methods of measuring the volume of a fluid in a container, such as floats or dip sticks, are not useful when a container changes shape as the printing fluid is used. This is the case for printing fluid bags which are designed to keep air from directly contacting the printing fluid. In this case, as the printing fluid is used, the ambient air pressure collapses the bag around the remaining printing fluid. This occurs non-uniformly such that the bag has no guaranteed shape as it collapses. Different methods have been proposed which would make the deformation more uniform allowing for a printing fluid level measurement by measuring the change in bag size. These methods include placing parallel plates on the sides of the bag which move towards each other as the bag collapses. A mechanical sensor or a capacitive sensor could be used to measure the separation of the plates from which the bag volume is calculated. These methods do not yield accurate estimates of the printing fluid volume.
The present invention proposes a different solution. The invention indirectly measures the amount of printing fluid in a printing fluid container by measuring the amount of air which can be placed into a fixed volume surrounding the printing fluid. Uniformity of container collapse for containers such as bags is no longer an issue. Also, the present invention allows fluid level sensing for bag containers where traditional fluid level sense techniques, such as floats or dip sticks, are difficult to use. Several possibilities exist for determining the amount of air and the volume it takes up at a particular temperature and pressure.
One aspect of the present invention relates to a fluid level detection system for determining the volume of fluid in a container (V.sub.FLUID). T his system includes a fluid container, a reference chamber that has a volume (V.sub.R), a pressure chamber in which the container is placed, the pressure chamber having a volume (V.sub.P), an air source, an air management system including at least one orifice, a pressure sensor that senses pressure, a time measurement device, and a computing device. The air management system is designed to selectively couple the air source to the reference chamber to pressurize the reference chamber to at least a first reference chamber pressure (P.sub.R1), to selectively couple the air source to the pressure chamber to pressurize the pressure chamber to at least a first pressure chamber pressure (P.sub.P1), to selectively couple the reference chamber to the orifice to discharge the reference chamber, and to selectively couple the pressure chamber to the orifice to discharge the pressure chamber. The time measurement device is designed to determine an elapsed time (.DELTA.t.sub.R) for a pressure in the reference chamber to drop from pressure (P.sub.R1) to a lower pressure (P.sub.R2), as sensed by the pressure sensor, and to determine an elapsed time (.DELTA.t.sub.P) for a pressure in the pressure chamber to drop from pressure (P.sub.P1) to a lower pressure (P.sub.P2), as sensed by the pressure sensor. The computing device is designed to determine a volume of air in the pressure chamber (V.sub.AIR) based upon the reference chamber volume (V.sub.R), the elapsed time (.DELTA.t.sub.R), the elapsed time (.DELTA.t.sub.P), and the pressures (P.sub.R1), (P.sub.R2), (P.sub.P1), and (P.sub.P2). Based upon this information, the computing device is also designed to determine the volume of fluid in the container (V.sub.FLUID) based upon the pressure chamber volume (V.sub.P) and the volume of air in the pressure chamber (V.sub.AIR).
Another aspect of the present invention relates to a printing device that includes a printing mechanism that prints an image, a printing composition, a container in which the printing composition is stored, a control system that enables printing by the printing mechanism, a pressure chamber in which the container is placed, the pressure chamber having a volume (V.sub.P), and a fluid level detection system for determining the volume of fluid in the container (V.sub.FLUID). The container is coupled to the printing mechanism to deliver the printing composition to the printing mechanism to print the image. The fluid level detection system is designed to determine the volume of fluid in a container (V.sub.FLUID) based upon the volume of air in the pressure chamber (V.sub.AIR). The fluid level detection system of the printing device may include those components described above in connection with the first aspect of the present invention.
The above-described aspects of the present invention may be modified as follows. The air management system may include a first orifice through which the reference chamber is discharged and a second orifice through which the pressure chamber is discharged. The time measurement device and the computing device may include a microprocessor or a controller that actuates the air management system to control selective coupling of the reference chamber to the air source, the pressure chamber to the air source, the reference chamber to the orifice, and the pressure chamber to the orifice. This microprocessor or controller is coupled to the pressure sensor to receive data representative of the sensed pressure points.
The air source may include a pump and the air management system may include conduit between the pump and the reference chamber, conduit between the pump and the pressure chamber, at least one valve, actuable to control pressurization of the reference and pressure chambers, conduit between the orifice and the reference and pressure chambers, and a valve, actuable to control depressurization of the reference and pressure chambers via the orifice. The container may include a bag and the pressure chamber may include an air-tight bag surrounding the container. The pressure sensor may include a first pressure sensor that senses pressures P.sub.R1 and P.sub.P1 and a second pressure sensor that senses P.sub.R2 and P.sub.P2. For the printing device, the air source may pressurize the pressure chamber to pressurize the ink during printing of the printing device.
Another aspect of the present invention relates to a method for determining the volume of fluid in a container (V.sub.FLUID) based upon the volume of air in a pressure chamber (V.sub.AIR) having a volume (V.sub.P). The method includes the steps of pressurizing a reference chamber having a volume (V.sub.R) to at least a first reference chamber pressure (P.sub.R1) discharging the reference chamber through a first orifice, sensing a decrease in pressure in the reference chamber from first reference chamber pressure (P.sub.R1) to a second reference chamber pressure (P.sub.R2) as the reference chamber is discharged, and determining an elapsed time (.DELTA.t.sub.R) for a pressure in the reference chamber to drop from pressure (P.sub.R1) to the pressure (P.sub.R2). The method also includes the steps of pressurizing the pressure chamber to at least a first pressure chamber pressure (P.sub.P1), discharging the pressure chamber through either the first orifice or a second orifice, sensing a decrease in pressure in the pressure chamber from first pressure chamber pressure (P.sub.P1) to a second pressure chamber pressure (P.sub.P2) as the pressure chamber is discharged, determining an elapsed time (.DELTA.t.sub.P) for a pressure in the pressure chamber to drop from pressure (P.sub.P1) to the pressure (P.sub.P2), determining the volume of air in the pressure chamber (V.sub.AIR) based upon the reference chamber volume (V.sub.R), the elapsed time (.DELTA.t.sub.R), the elapsed time (.DELTA.t.sub.P), and the pressures (P.sub.R1), (P.sub.R2), (P.sub.P1), and (P.sub.P2). From this information, the volume of fluid in the container (V.sub.FLUID) is determined based upon the pressure chamber volume (V.sub.P) and the volume of air in the pressure chamber (V.sub.AIR).
The above-described method may additionally include the step of refilling the container with the fluid if the volume of fluid in the container (V.sub.FLUID) is either at a predetermined level or below a predetermined level. The above-described method may further include the step of signaling prior to refilling, if the volume of fluid in the container (V.sub.FLUID) is at the predetermined level or below the predetermined level.
Another aspect of the present invention relates to an apparatus for use in a printing device that includes a container in which a printing composition is stored, a printing composition port coupled to the container for supplying printing composition from the container to the printing device, a pressure chamber in which the container is placed, the pressure chamber being configured to be airtight and to define a fixed volume, and an air port coupled to the pressure chamber. The air port is configured to supply air to the pressure chamber to pressurize the fixed volume of the pressure chamber.
The above-described apparatus may be modified as follows. The pressure chamber may include an airtight member and a body in which the airtight member is placed. The body limits expansion of the airtight member to the fixed volume during pressurization of the pressure chamber. The airtight member may include a bag or a shell. The container may include a first bag and the pressure chamber may include a second bag. The container may be removably placed in the pressure chamber so as to be separable therefrom. The air port may include a bidirectional valve actuable in a first direction to pressurize the pressure chamber and actuable in a second direction to depressurize the pressure chamber. The apparatus may further include an interconnect having a first conduit that couples to the container and the printing device to supply printing composition to the printing device, and a second conduit that couples to the pressure chamber and an air source to pressurize the pressure chamber. This interconnect is designed to couple the pressure chamber to the source after the container is coupled to the printing device to help prevent spilling of printing fluid.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.